Laser Micromachining And Mechanism Research Of Wide Bandgap Materials

The research and application of wide band-gap materials get more and more attentions by schoolar, such as silica glass (SiO2) and the representative of the third generation semiconductor materials--gallium nitride (GaN) materials have become the research focus. Because of its excellent physical properties, fused silica has become one of important material for fabrication of MOEMS devices. GaN-based semiconductor material which has characteristics of high electron saturation drift velocity, good thermal conductivity and other properties, has become key material of the LEDs light-emitting semiconductor devices, and its application prospect is very broad.However, they are difficult to machine because of chemical inertia and the mechanical propertis of brittle and hard. The 157nm deep-ultraviolet laser is of short wavelength and large single photon energy, so that it can directly destory the chemical bond of many materials, and the thermal-effect region is very small. Hence, 157nm laser is an ideal tool for machining fuled silca and GaN materials.In this paper, a 157nm DUV laser micro-machining system (M2000-type) and its processing performance are described. Using the system, a series of micro-etching experiments are conducted for wide band gap materials, such as fused silica, optical fiber and GaN film. And their micro-etching mechanisms are discussed. The main research content and conclusions are as follows:1. For fused silica, the ablation depth and surface roughness are investigated after 157nm laser processing. Experimental results show that, with increasing of laser shot numbers, the ablation rate of fused silica would reduce gradually. The lager laser spot is preferable to enhance the ablation rate. The laser repetition rate is preferably not more than 25Hz for improving the quality of ablated micro-holes. According to the results and using the optimum process parameters, several three-dimensional microstructures are produced in silica glass chip, which confirmed that 157nm laser is available on manufacturing MOEMS devices. In addition, a variety of three-dimensional microstructures are fabricated in fiber (sigle-mode and muti-mode), which would provide a new technology for fabricating the new-type fiber-optic sensor.2. Using excimer laser with 157nm wavelength, experimental investigations on micro-ablation of LED-GaN semiconductor films are carried out, the range of optimum process parameters is determined. Combined with numerical control technology, several three-dimensional microstructures are trial-produced in the GaN film. The influence of process parameters on the angle of side wall is also researched. The results show that,157nm laser is of stronger ability on machining 3D micro-structures of GaN material.3. The primary etching performance and mechanism of two important wide band-gap materials are studied, and the mathematical models are established. Analysis show that, photo-chemical reaction induced by single photon absorption plays a dominant role in 157nm laser process of fused silica and GaN material.